SQL-DATABASE ERROR

Database error in WoltLab Burning Board (): Link-ID == false, connect failed
mysql error: Unknown MySQL server host 'mysql5.service' (1)
mysql error number: 2005
mysql version: unknown
php version: 4.4.8
Date: 15.07.2018 @ 20:52
Script: /memberslist.php?sid=893e871e2fa0d80bd252a2b4cd3afd3e
Referer: